Convert an absolute path to a relative one.
CL_String CL_VirtualDirectory::make_path_relative( const CL_String & absolute_path);
Detailed description:
If CL_VirtualFileSystem was not set, this function uses CL_PathHelp::path_type_file If CL_VirtualFileSystem is set, this function uses CL_PathHelp::path_type_virtual param: absolute_path = The absolute path